Repairing Heidenhain MT30 probe retraction mechanism

I recently got a Heidenhain MT30 indicator probe. This has 30mm of travel and 1 micron resolution, and works very nicely with a bunch of my dated readout equipment.

There is one thing that bugs me. The probe came with a ~50 cm long pushbutton-on-a-cable thing that is meant to retract the probe, but it doesn't work. So I took it apart today to see what was happening. The pushbutton/cable thing drives the rack gear of a small rack-and-pinion assembly; the rack was jammed, and I freed it. But there are signs that others have been here before, and did not leave everything behind, so I can't tell for sure how it works.

I think the way this works is that the pinion gear (not visible, on the other side) drives the lower aluminium wheel shown in the photo below. That wheel is supposed to be tensioned by a small string and spring. Then another bit of string that pulls the probe rides by friction on the same wheel. I found one bit of broken string still attached to the aluminium wheel, but no spring or other bits. The photo below shows what this looks like.



If someone here has one of these MT30 probes on hand, could you please remove the cover (two small screws) and take a photo of the innards for me, so I can see how it is supposed to work?

Cheers,
Bruce

I would really be grateful for a photo of the inside. Hasn't someone here got one of these?


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Well I ended up buying another one of these probes, because it was for sale on Ebay for a very good price. So I had a look to see how it works.










There are two separate "string" mechanisms or circuits.

(1) On the lower (smaller diameter) part of the big wheel a piece of string is wound around, which runs over a small pulley and then to a tensioned coil spring. This tries to rotate the big wheel in the clockwise direction. The loop, visible on that big wheel, which is locked with the brass clip, secures this piece of string to the big wheel.

(2) On the upper (larger diameter) part of the big wheel, a piece of string is wound around which passes over the upper pulley, then connects to the moving "sled" of the scale, and then returns to the big wheel again. This keeps the scale sled in the downmost position to extend the scale plunger to the maximum extent. This string passes through the notches in the big pulley, to keep it from slipping, and then is secured with the blob/drop of black paint visible on the top of the big wheel.

I was able to fix the mechanism using dental floss as the "string" and winding my own spring. For the record, the spring is made from 0.3mm spring steel, and has an OD of 3.5mm and an overall length (relaxed) of about 27mm.

Cheers,
Bruce